Ascorbic acid ester antistain agents



United States Patent 2,728,661 7 ASCORBIC ACID ESTER ANTISTAIN AGENTS John B. Thirtle, Ilmari F. Saiminen, and Arnold Weissberger, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey I No Drawing. Application October 16, 1953, Serial No. 386,672

11 Claims. (Cl. 95-6) This invention relates to color photography and particularly to a method for preventing the formation of color fog or stain in photographic emulsions.

The method of color photography in which color-forming or coupler compounds'combine with the develop ment product of aromatic amino photographic develop- ;ers to produce dyes is well known. The color formers or couplers may be added directly to the emulsion layers or may be incorporated in the developing solution as described in Fischer U. S. Patent 1,102,028, granted June 30, 1914, or they may be incorporated in a Water-permeable medium which is insoluble in the carrier for the sensitive silver salt as described in Mannes and Godowsky U. S. Patent 2,304,940, December 15, 1942, and Jelley and Vittum U. S. Patent 2,322,027, granted June 15, 1943.

A difiiculty frequently encountered in these processes is the formation of color fog or stain. When the exposed material is developed in a color-forming developer, dye fog is frequently formed in the emulsion layer. This is because the developing agent has been oxidized to some extent by the action of the air and the oxidized developer tends to couple with the color-forming compound at places in the photographic material where no silver image is produced. It is well known that in these processes the dye should be formed only where the silver halide is reduced to metallic silver, thereby oxidizing the developing agent to a form which couples with the color former. Once the developing agent is oxidized, it couples immediately with the color former whether a photographic image is present or not. Aerial oxidation of the developer or oxidation by means of other than the photographic image therefore converts the developer to a form which will immediately react with the color former to produce a color fog or stain. This efiect is especially noticeable in materials having couplers incorporated in the sensitive layer since there is no coupler in the developing solution to react with any developing agent which is oxidized by the action of the air. Fog or stain arising from these causes is not readily controlled by the same procedures used to control silver fog.

The control of color fog or stain by incorporating hydroquinone or certain of its derivatives, e. g., diamyl or dioctyl hydroquinone, in photographic emulsions is described in Vittum and Wilder U. S. Patent 2,360,290, granted October 10, 1944. The use of ascorbic acids for this purpose is described in'Vittum and Wilder U. S. Patent 2,401,713, granted June 4, 1946. The ascorbic acids have not, however, been incorporated in photographic emulsion layers because of their low solubility in organic solvents and migration during processing, thus preventing their effective use as antistain agents.

It is therefore an object of the present invention to provide a novel class of antistain agents which improve stability of the color developed dye image to heat and light. A further object is to provide antistain agents which may be dissolved in organic solvents and which are non-difiusing in the colloid of the photographic layer in which they are incorporated. A further object is to provide antistain agents which are strong enough reducing agents to react rapidly with oxidized color developer. A further object is to provide water-soluble, non-diifusing ascorbic acid esters. A further object is to provide antistain agents which do not form highly colored oxidation products when the material containing them is put through an oxidizing bath. Other objects will appear from the following description of our invention.

These objects are accomplished by the use in an emulsion layer or other layer of a photographic material especially a silver halide emulsion layer in which a colored image is formed by development in a color forming developer, of an ascorbic acid ester having the formula Lin -0H 4 in isidnx (a) (into c 0 R in which R=alkyl aryl sulfonated alkyl or aryl carboxylated alkyl or aryl R=an alkyl group of 7-18 carbon atoms an aralkyl group of 7-30 carbon atoms a mononuclear aryl group This formula represents the structure but not the stereochemical configuration.

The following examples are illustrative of derivatives soluble in organic solvents:

Lii-OH (EH HOH JHzO C 0 011112:

fi-l-ascorbyl Iaurate iL-OH La JHOH GHQO C O C1 Ha1 G-d-isoascorbyl palmitate OH il-0H in H0 H (ilHgO C O 6-l-ascorbyl benzoate We may also use 6-l-ascorbyl caprylate, 6-l-ascorbyl myristate and 6-l-ascorbyl stearate.

The following examples of our invention are ascorbic acid esters containing solubilizing groups, making them suitable for direct incorporation in photographic gelatin or water-permeable colloid layers:

n... s 03H H I 3 O C 0 (51110 C OCH31 Ascorbyl 6-palmitate 5-o-sulfobcnzonte 0H Lil-4m (EH ABHO C O CHzCHaSOaH $1120 0 O CisHai Ascorbyl G-palmitate E-Beulfopropionate (L0H L &OH

H S 0 aH (iTHO C O CHnH-CrsHar Ascorbyl fi-palmitate 5-B-sulfostearate L-OH Lff 0 0 on u ,1 (hHO C 0 H2O C 0 01511 Ascorbyl fi-palmitate 5-o-carboxy-benzoate (8) 0:0 7

QH l OH 5H EHO O 0 CHzCHzC O OH 3311 0 0 O CisHai Ascorbyl G-palrnitate 5-!3-carboxy-propionate All of these ascorbic acid esters contain free hydroxyl groups which appear to render emulsions containing the compounds somewhat unstable on storage prior to exposure and processing. This can be overcome by acylating the hydroxyl groups prior to incorporating the compounds in the emulsion. The ester will be hydrolyzed to an efli'ective antistain agent at the time of processing in the alkaline developer solution. This hydrolysis apparently affects only the ene-diol groups in the 2 and 3 positions.

The following compound illustrates an ester acylated in this way:

(|JOCOCHa LiIB-OOOCHa HOCOCH:

HqOCOC Hal Ascorbyl-2,3,5-triacetate-6-palmitate The ascorbic acid esters of higher aliphatic acids, e. g., Compounds 1 and 2, were prepared by the reaction of ascorbic acid with the corresponding aliphatic acid in the presence of sulfuric acid, as described in U. S. Patent 2,375,250.

The sulfonated esters, e. g., Compounds 4, 5 and 6, were prepared by heating the ascorbic acid ester, e. g., ascorbyl-6-palmitate, with the appropriate acid anhydride, e. g., o-sulfobenzoic anhydride, fl-sulfopropionic anhydride, or B-sulfostearic anhydride.

The carboxyl-solubilized esters, e. g., Compounds 7 and 8, were prepared by reacting the ascorbic acid ester, e. g., ascorbyl-6-palmitate, with the appropriate acid anhydride, e. g., phthalic anhydride or succinic anhydride, in the presence of a trace of zinc chloride.

The triacetate, Compound 9, was prepared as described in U. S. Patent 2,454,747.

The organic solvent-soluble antistain agents of our invention are useful, in general, with emulsions containing couplers incorporated in the manner described in Mannes and Godowsky U. S. Patent 2,304,940 or Jelley and Vittum U. S. Patent 2,322,027.

The alkali-soluble antistain agents of our invention are useful, in general, with emulsions containing couplers incorporated in the manner described in Fischer U. S. Patent 1,102,028.

Couplers such as those described in Weissberger U. S. Patent 2,298,443 and Salminen and Weissberger U. S. Patent 2,423,730, when incorporated in emulsions, produce dyes upon color development which are prone to fading by the action of visible or ultraviolet light, when known antistain agents such as 2,5-di-tert. octyl hydroquinone are used in the emulsion layer. These are the yellow and cyan dyes. The magenta dyes, such as those formed from couplers described in Loria, Weissberger and Vittum U. S. Patent 2,600,788 are relatively little affected by the known antistain agents upon the action of light.

In order to illustrate the eifect of our antistain agents, the following test was made.

A quantity of the antistain agent, the molar equivalent of 0.05 g. of 2,5-di-tert. octyl hydroquinone, was dissolved with 0.5 g. of coupler in 1.5 cc. of dibutylphthalate. To this solution was added 11 cc. of 10% gelatin solution and 2.8 cc. of 5% Alkanol B (sodium alkyl naphthalene sulfonate) solution. The resulting mixture was passed through 'a colloid mill three times, and to the resulting dispersion, 32 cc. of a gelatino-silver halide emulsion were added, and the mixture blended and coated on a film support so that the antistain agent was equivalent to 5 mg. per square foot of 2,5-di-tert. octyl hydroquinone.

Two check coatings were made: One containing no antistain agent, and one containing 5 mg. per square foot of 2,5-di-tert. octyl hydroquinone.

The film strips were exposed on an Eastman I-b Sensitometer using a silver wedge varying in density from 0 Water to 1 liter.

This was followed by ;5 min. in the following stop bath:

Sodium sulfite (desiccated) s g Acetic acid (28%) ..c c 235 Boric acid, crystals v ,g 27.5 Potassium alum g 75 Water to 1 liter.

After washing, bleaching in ferricyanide-bromide, fixing in 30% hypo solution and again washing, {the wavelength-density curves for each coating were read before and after exposure in the Fade-O-Meter' for 6 hours. From the resulting curves the loss in density at maximum absorption of the resulting dye, as shown by a plot of density against wave-length, were determined. The following table shows these results:

Loss in density at maximum absorption These results show that both of the agents cause less fading of the cyan and yellow dyes than that caused by 2,5-di-tert. octyl hydroquinone.

The antistain agents of our invention may also be used in non-senitive overcoating or filter layers, such as a colloidal silver interlayer of multilayer photographic material. In general, the antistain agents of our invention are used in the emulsion or other layer in quantities ranging from 0.07 gram to 4.3 grams per liter of emulsion or gelatin solution. These values are, however, merely illustrative.

In certain cases the antistain agents of our invention may be incorporated in a processing solution such as a prebath, first developer bath, or color-forming developer used with color film which is developed with a primary aromatic amino developing agent.

Our materials are particularly useful with color-forming emulsions coated on paper supports where it is especially important to reduce the minimum or fog densities. This applies both to negative developed paper and to reversal paper as well as to transparency materials.

It will be understood that the examples and modifications described herein are illustrative only and that our invention is to be taken as limited only by the scope of the appended claims.

We claim:

1. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diffusing coupler compound and as an antistain agent an ascorbic acid ester having the formula -OH Lin where X is selected from the class consisting of hydroxyl and -OCOR radicals, R is selected from the class consisting of alkyl radicals, aryl radicals, sulfonated alkyl radicals, sulfonated aryl radicals, carboxylated alkyl radicals and carboxylated aryl radicals, and R is selected from the class consisting of alkyl radicals containing from 7 to 18 carbon atoms, aralkyl radicals containing from 7 to 30 carbon atoms, and mononuclear aryl radicals, and the enediol esters of said compounds.

2. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diffusing coupler compound and as an antistain agent an ascorbic acid ester having the formula i l-OH La HOB HsOCOR in which R is an alkyl group containing from 7 to 18 carbon atoms.

3. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diffusing coupler compound and as an antistain agent an ascorbic acid ester having the formula:

in which R is a sulfonated alkyl group and R is an alkyl group of from 7 to 18 carbon atoms.

4. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diffusing coupler compound and as an antistain agent an ascorbic acid ester of an aliphatic acid containing from 7 to 18 carbon atoms.

5. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diffusing coupler compound and as an antistain agent 6-1-ascorbyl laurate.

6. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diffusing coupler compound and as an antistain agent 6-d-isoascorbyl palmitate.

7. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diifusing coupler compound and as an antistain agent ascorbyl 6-palmitate S-o-sulfobenzoate.

8. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-difiusing coupler compound and as an antistain agent ascorbyl 6-palmitate 5-,3-sulfopropionate.

9. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diffusing coupler compound and as an antistain agent ascorbyl 6-palmitate S-fi-sulfostearate.

10. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diffusing coupler compound and a completely esterified ascorbic acid ester as an anti-stain agent.

11. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-difiusing coupler compound and ascorbyl-2,3,5-triacetate-6-palmitate as an anti-stain agent.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A COLOR-FORMING PHOTOGRAPHIC EMULSION HAVING REDUCED FOGGING TENDENCY, COMPRISING A SILVER HALIDE EMULSION HAVING INCORPORATED THEREIN A NON-DIFFUSING COUPLER COMPOUND AND AS AN ANTISTAIN AGENT AN ASCORBIC ACID ESTER HAVING THE FORMULA WHERE X IS SELECTED FROM THE CLASS CONSISTING OF HYDROXYL AND -OCOR RADICALS, R IS SELECTED FROM THE CLASS CONSISTING OF ALKYL RADICALS, ARYL RADICALS, SULFONATED ALKYL RADICALS, SULFONATED ARYL RADICALS, CARBOXYLATED ALKYL RADICALS AND CARBOXYLATED ARYL RADICALS, AND R'' IS SELCETED FROM THE CLASS CONSISTING OF ALKYL RADICALS CONTAINING FROM 7 TO 18 CARBON ATOMS, ARALKYL RADICALS CONTAINING FROM 7 TO 30 CARBON ATOMS, AND MONONUCLEAR ARYL RADICALS, AND THE ENEDIOL ESTERS OF SAID COMPOUNDS. 